This invention relates to a new improved center conductor female element for a miniature female coaxial connector.
Present day requirements in microwave systems and components are leading to the continually increasing use of higher and higher frequencies for coaxial microwave systems and components. In order to provide mode free performance at these higher frequencies, it has been necessary to make connectors physically smaller. The commonly used SMA connector is an example of a minature coaxial connector that can be used at higher microwave frequencies. The SMA is a sexed connector that is usable to 26 GHz.
Recently, a new high performance 3.5 mm sexed coaxial connector, commonly known as the APC-3.5 and manufactured by the Amphenol Division of Bunker Ramo, has been introduced that gives mode free performance to 34 GHz, see S. F. Adam, G. R. Kirkpatrick, N. J. Sladek, S. T. Bruno, "A High Performance 3.5 mm Connector to 34 GHz," Microwave Journal, Vol. 19, No. 7, July 1976. The APC-3.5 is a coaxial connector pair comprising a male and female connector, each element of which is compatible with the standard type SMA connector now commonly used. Unlike the SMA, the APC-3.5 is an air dielectric connector. That is, in the vicinity of the male-female center conductor connection, air is the dielectric in the region between the center conductor and outer conductor.
The APC-3.5 was designed to provide improved electrical performance, mechanical ruggedness, and reliability to the type SMA. It does provide improved electrical performance. However, the female connector has been found to have an unacceptably high failure rate with repeated usage. This is caused by both mechanical distortion and failure of the center conductor female element. The APC-3.5 female element is slotted to provide four fingers that are resiliently biased toward each other so that, when the male pin of the mating connector is inserted, positive contact is made at the ends of the fingers. When failure occurs, the cause is usually found to be that at least one of the female fingers is not making contact, at its end, with the male pin. This causes undesirable electrical reflections which typically become severe, or resonate, at frequencies above 10 GHz.
The failure mechanism can be explained as follows: Due to nominal design clearances and dimensional tolerances, there can be quite a bit of play or "slop" in the mating of APC-3.5 and SMA connectors. This play allows the SMA or APC-3.5 male connector pin to engage either off center or at an angle with respect to the APC-3.5 female element. The APC-3.5 connector has outer and inner conductor diameters of 0.138 inch (3.5 mm) and 0.060 inch respectively which make the female element fingers too fragile (approx. 0.011 inch thick) to forcibly center the mating male pin. Either of the situations is illustrated in FIGS. 1 and 2 of the drawing herein and can cause one or more of the female element fingers to be deflected as shown, and not make contact at their ends with the male pin. Once a female element finger has been distorted, as illustrated in FIGS. 1 or 2 of the drawing, it will usually not make contact, at its end, on later connections even though the male and female elements are centered. This is because severe deflections take the fingers past the point where they can recover and spring back to their original position. This type of female element failure does not occur in the SMA female connector because the female element of the SMA connector is surrounded by a plastic dielectric (typically teflon) that prevents the fingers from being distorted outwardly as shown in FIGS. 1 and 2 of the drawing.
One solution to the female element failure problem for miniature air dielectric coaxial connectors was proposed by Wiltron Co. and is described in an article entitled "Connector Relieves Nagging SMA Measurement Problems" Microwaves, Vol. 18, No. 1, January 1979, pp. 97-99. As described, the female element consists of two concentric tubes, with the inner tube slotted, to form fingers which are biased to make contact with both the outer tube and the mating male pin. The outer tube is unslotted and prevents the fingers from being distorted outward by an off-center male pin. However, this solution is not entirely satisfactory since the female element is difficult and costly to manufacture, requiring extremely tight dimensional tolerances and complicated twisted biasing of the fingers.